1. Field of the Invention
The present invention relates to a stepping motor driving device, a lens driving device, and a camera.
2. Description of the Related Art
Cameras manufactured today optically correct a shake, such as a camera shake caused by hand-held shooting, to thereby achieve shooting free from the shake. More specifically, such conventional cameras use means for driving a shake correcting lens in any direction orthogonal to an optical axis according to a signal from shake detecting means, such as a gyro sensor, to thereby prevent occurrence of image blur on an image forming surface.
An image blur preventing mechanism 20 shown in FIG. 5 can be mentioned as a first prior art example related to the image blur preventing technique (see Japanese Laid-Open Patent Publication (Kokai) No. H05-203895).
According to this image blur preventing mechanism 20, the rotational angle of a first motor is controlled, for example, based on information on a shake detected by shake detecting means, whereby an output from the motor causes first conversion means to displace a shake correcting lens in a first direction for shake correction. Similarly, displacement of the shake correcting lens in a second direction is caused by a second motor.
Further, a time-sharing drive apparatus for a motor of a camera, which is disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H10-197779 (corresponding to U.S. Pat. No. 6,014,523) can be mentioned as a second prior art example. This time-sharing driving apparatus is for a camera equipped with more than two motors, and includes motor driving control means for alternately driving the motors in a time-sharing manner.
With this configuration of the apparatus, it is possible to provide a time-sharing driving apparatus for a motor of a camera, which is reduced in power consumption, particularly in maximum power consumption.
Furthermore, a stepping motor driving device disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H10-313593 can be mentioned as a third prior art example. This stepping motor driving device is configured to control a plurality of stepping motors based on data stored in advance. More specifically, the stepping motor driving device drives the stepping motors of a single-phase excitation type in a time sharing manner within a predetermined processing time period based on the data stored in advance.
With this configuration, it possible to reduce electric power consumed for driving the stepping motors simultaneously, without superposing exciting currents flowing through driving coils when using the stepping motors by driving them at a relatively low speed.
In each of the above second and third prior art examples, a description is basically given of a case where a plurality of stepping motors drive respective different lenses, such as a zoom lens for a zooming operation and a focus lens for a focusing operation. However, the apparatus or device can also be applied to the image blur preventing mechanism mentioned as the first prior art example, in which the single camera shake correcting lens is driven by the two stepping motors, so as to provide the same function.
In the image blur preventing mechanism in the first prior art example disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H05-203895, it is required to always drive the shake correcting lens during execution of shake correction, and hence electric power is always consumed by the driving means, which causes an increase in the total power consumption of the camera.
Further, in still image shooting, in addition to shake correction required during an exposure operation so as to achieve shooting free from shakes, shake correction performed during an aiming operation which generally takes longer time than an exposure operation consumes the same amount of electric power, which causes an increase in power consumption in a single shooting operation.
Furthermore, in a camera which is capable of switching between still image shooting and moving image shooting, a larger amount of electric power is consumed in moving image shooting, where shake correction is always required, than in still image shooting.
What is more, the power consumption is constant during execution of shake correction, irrespective of shake speed. More specifically, in either of a case where the shake speed is high and the stepping motors are driven at a high speed and a case where the shake speed is low and the stepping motors are driven at a low speed, power consumption hardly changes, and hence unnecessary electric power is consumed when the stepping motors are driven at a low speed.
To eliminate these inconveniences, it is possible to reduce power consumption by using the motor driving apparatus or device shown in the prior art example 2 or 3. However, in the disclosed methods of driving motors in a time-sharing manner, time lag occurs between detection of a shake and the start of motor driving, which causes marked degradation of shake correcting performance.